1. Field of the Invention
The present invention relates generally to control devices for interfacing with and manipulating the position of graphical objects generated on a computer display, and more specifically to an optically transmissive armature for providing an improved optical pathway for light signals representative of the movement of a cursor control device.
2. Brief History
A standard component of today's computer controlled display systems is a cursor control device, external from an ordinary keyboard, commonly referred to as a "mouse." A typical mouse is a hand-held device which allows a user to control the position of a cursor on an associated display by simple translational movement of the mouse body and associated roller-ball over a frictional surface.
State of the art cursor control devices usually operate by manipulating beams of light within the device body in a manner such that the affected light signals are representative of the translational movement of the device across a surface. An example of this type of cursor control device is presented in U.S. Pat. No. 4,464,652, which is hereby incorporated by reference. The device as described therein uses encoder wheels, each of which includes a roller shaft frictionally coupled to the roller-ball of the device. In one common configuration, two encoder wheels are utilized and include associated roller shafts positioned at substantially 90 degrees relative to one another. When the roller-ball is rolled over a surface, depending on the direction of motion of the ball, the roller shafts will rotate and spin the attached encoder wheels. If the ball is rolled exclusively in a first translational direction, for example, along an imaginary x-axis, only a single roller shaft and associated wheel will rotate. If the ball is rolled exclusively in a direction perpendicular to the first direction, for example, along an imaginary y-axis, the other roller shaft and associated wheel will rotate. Movement of the ball in a combination of these x and y directions will cause both shafts and associated wheels to rotate.
The encoder wheels each have a plurality of radially disposed slots towards their outer peripheries. Light beams, produced by photo-emitters, intermittently pass through the slots as the encoder wheel rotates and are received by carefully aligned photo-detectors. Each wheel is positioned between two pairs of photo-emitters and photo-detectors and assiduously arranged such that, when the light beam from a first photo-emitter is fully transmitted through one of the slots, the other beam from the second photo-emitter is partially blocked by the body of the wheel. Beam interruptions produce signal pulses representing increments of motion, while the order in which the light beams are interrupted indicates the direction of motion. These signal pulses are translated into computer code and direct the cursor on the computer display to track the movement of the cursor control device.
A significant problem with this type of device is that the optical and mechanical components require extremely precise alignment. Indeed, the single largest reason for functional rejects in the manufacture of cursor control devices, i.e., mice and trackballs, is insufficient alignment of the optics. And, not only do the photo-emitters and photo-detectors require precise relative alignment, but the encoder wheels must also be precisely aligned relative to each of the photo-electrical components in order to assure proper device performance.
An additional drawback with this type of device is that it cannot be reliably manufactured robotically without custom automation. Because the optical encoding assemblies must face each other, they cannot be surface mounted, and pick-and-place machines cannot be used. A custom robot is required for each assembly, or, alternatively, an additional subassembly must be created which requires a separate automatic manipulator to provide for full automation. This significantly increases production costs and time, and decreases associated product reliability.